Will new advances in prenatal testing shrink the ranks of babies with Down syndrome?

The new face of the Down-syndrome family. Becker reads to her daughter Penny, who has Down syndrome, and her son. Becker's book is about raising a child with the condition.

Pregnant with her third child at 40, Melanie Perkins McLaughlin, a documentary filmmaker from outside Boston, did what many women in her situation do: after much agonizing, she had her swollen belly pricked by a long needle so her doctor could draw a bit of her amniotic fluid and tell her whether her unborn baby had Down syndrome.

She had a good statistical reason to take the test: 1 in 100 pregnancies in her age group results in Down syndrome. A questionable ultrasound finding had upped her risk to 1 in 5, but that also meant a 4 in 5 chance...